There is a technique of detecting a heartbeat of a biological object by using a heartbeat sensor. A bandpass filter (BPF) is applied to a detected signal of the heartbeat sensor to detect a signal component corresponding to the heartbeat from the detected signal of the heartbeat sensor.
Further, a heartbeat of a biological object varies in a time length of one heartbeat according to whether a heart rate per unit time is high or low. Therefore, BPF characteristics (e.g. pass center frequency and a passband width) may be varied depending on whether the heart rate is high or low.